1. Field of the Invention
The present invention relates to optical devices and methods for producing the devices, and specifically to an optical device having an improved optical interconnection structure between optical waveguides and optical elements and a method for producing the device.
2. Description of the Related Art
Optical interconnection technology has recently been introduced to electronic circuit boards for electronic devices to achieve higher signal transmission speeds. Specifically, an optical waveguide is stacked on an electronic circuit layer for use as an optical interconnect in a circuit board. A circuit board having both electronic and optical interconnects is generally called an optical electronic integrated circuit board.
FIG. 2 shows an example of an optical electronic integrated circuit board. In FIG. 2, an optical electronic integrated circuit board 200 includes a printed circuit board 10 including optical waveguides 11 and an IC-chip mounting substrate 20 on which a vertical cavity surface-emitting laser (VCSEL) 22 and a photodiode (PD) 23 are mounted. The IC-chip mounting substrate 20 is flip-flop mounted on the printed circuit board 10 with bump electrodes 31 and soldering balls 32 disposed therebetween. This optical electronic integrated circuit board 200 is used as an optical device by connecting it to an optical fiber (not shown) through a connector 40. An important challenge for such optical devices is the reduction of connection loss between optical components.
As examples of techniques for improving such optical devices, Japanese Unexamined Patent Application Publications No. 2004-4426 and 2004-4427 (see, for example, the claims of the publications) disclose optical communication devices that include an underfill layer for optical paths or optical signal transmission lines through which optical signals are transmitted between optical waveguides and optical elements to reduce the connection loss between optical components and achieve excellent connection reliability. In addition, Japanese Unexamined Patent Application Publication No. 2001-185752 (see, for example, the claims of the publication) discloses a technique for reducing optical loss by providing microlenses in an optical path of signal light between a surface-emitting element and an optical waveguide. Another technique is the use of right-angle bending elements for reducing optical loss.
As described above, various techniques for reducing connection loss between optical waveguides and optical elements have been proposed. The techniques using microlenses or right-angle bending elements, however, have difficulty in positioning them when they are mounted on an optical electronic integrated circuit board. In the mounting of optical elements on the circuit board, additionally, the positions thereof must be adjusted to those of the microlenses or the right-angle bending elements mounted on the circuit board. As a result, such techniques undesirably involve a larger number of steps for mounting. Furthermore, foreign matter can intrude into an optical path of signal light, obstruct transmission, and cause optical loss.
The transmission of optical signals between optical waveguides and optical elements through an underfill layer for optical paths or optical signal transmission lines, as disclosed in the above publications, is unsatisfactory, and techniques for optical connection with lower loss are demanded.